This invention relates to a catalyst for the catalytic combustion of hydrogen. More particularly, this invention relates to an oxide catalyst which enables hydrogen to undergo complete combustion easily at a relatively low temperature whereat the combustion of hydrogen does not reach flame combustion.
Scientists know that humans will eventually have to stop relying on fossil fuels and have long been giving attention to hydrogen as a fuel that shows every promise of being accepted for large-scale use by the general public in the future.
It has been found by the present inventors that when the amount of air pre-mixed hydrogen is small, the combustion gives rise to a large amount of nitrogen oxides (NO.sub.x). When the amount of pre-mixed air is large, the combustion suffers from the phenomenon of backfire even though the NO.sub.x emission level is markedly reduced. Thus, it has been found very difficult to obtain safe combustion of hydrogen without entailing the danger of air pollution.
For the purpose of eliminating this difficulty and in due consideration of the fact that hydrogen is more readily combustible than any other fuel, attempts have been made to develop a catalyst which enables combustion of hydrogen to proceed safely at low temperatures. Test results have been ascertained that catalysts of platinum-group metals are most effective in realizing such ideal combustion of hydrogen. Unfortunately, platinum-group metals are very expensive and are not likely to be available in quantities that fill the demand when catalytic heaters using hydrogen have come into use on an extensive scale.
It has been ascertained, on the other hand, that some of the oxides of transition metals which are inexpensive and readily available can be used as catalysts for the catalytic combustion of hydrogen, although they are inferior to the platinum-group metals in catalytic activity. Silver oxide exceeds all the other oxides of transition metals in terms of the magnitude of initial catalytic activity. Once it is exposed to a temperature exceeding 150.degree. C., however, it is partially decomposed to silver and consequently loses its catalytic activity almost completely.
An object of this invention is to provide a catalyst for the catalytic combustion of hydrogen which is capable of exhibiting high catalytic activity over a wide range of temperatures from low to high degrees.
Another object of this invention is to provide a catalyst for the catalytic combustion of hydrogen, which comprises materials inexpensive and available virtually inexhaustibly.